Popplewell, eldest of three children, is the daughter of Andrew Popplewell QC and Dr. Debra Lomas, an immunologist. Her paternal grandfather, Sir Oliver Popplewell, is a distinguished former judge. She attended North London Collegiate School and was senior student 2006-2007.

Since 2007, Popplewell has been a student of English at Magdalen College, Oxford. She was awarded the Cuppers Prize in 2007, for Best Supporting Actress, in a student production of Five Kinds of Silence. In December 2007, she played Lady Macbeth in a student production of Macbeth at the OFS Studio in Oxford.